1. Field of the Invention
The present invention relates to a distance detecting apparatus for obtaining a distance measurement of an object using triangulation. This apparatus detects two photo-currents are output from a light sensitive element, in proportion to an image position determined by a reflected light from the object on the photosensitive element surface. An integration operation is then conducted to give a distance signal. The present invention can be adjusted for slippage from a calibrated position of the light-receiving sensor by means of electrical adjustment.
2. Description of the Prior Art
Various proposals and practical uses have been made heretofore to detect the distance of an object in automated triangulation. But, in the principle of measurement by a distance detecting apparatus, a position of a beam spot on a light receiving sensor (PSD) formed by light reflected by an object must be in a designed reference position which is apart by a predetermined distance from the center of the PSD (the center is on the optical axis). When a focused spot is formed accurately on the reference position of an optical system thereof, the PSD outputs an accurate measurement data of distance information. However, if an electrical center of light receiving sensor is not set up accurately at an optical axis of the light receiving optical system, the image forming position does not correspond to an accurate distance to an object.
Causes of the failure of an electrical center of a light receiving sensor correspond with the fixed reference position is attributable to the displacement of the set-up position of the sensors, and the displacement of the sensors themselves. In the prior art, calibration is conducted by appropriate movement of the light emitting element or of a light receiving sensor so as to output a predetermined signal corresponding with fixed distance of an object. In the prior art, the position deviation of the light-receiving sensor due to inaccuracy of assembly has been corrected by, after once by trially shifting the light emitting element or light receiving sensor so that an appropriate output signal is issued for an object of a predetermined distance.
However, the adjustment operation mentioned above needs very fine movement of the light receiving sensor and the light emitting element. As microscopic movement mechanism have to be set up in the apparatus, the adjustment operation is complicated operation and much attention have to be paid for the complicated operation.
In order to solve the above-mentioned problem, for example, a proposal disclosed in Gazette of Patent unexamined Publication No. Sho 60-211412 issued Oct. 23, 1985 has been made. Therein, a distance detecting apparatus for adjusting the above-mentioned slippage through electrical adjustment is disclosed.
In the above-mentioned prior art shown FIG. 1, a position sensitive detector (PSD) is used as light receiving sensor; and a variable resistor is connected in an electric path of anode A.sub.2. The beam spot S moves farther away from the electrical center as the object comes nearer. FIG. 1, shows a state that the electrical center C of position sensitive detector PSD 1 is shifted from the optical axis L of the light-receiving optical system (not shown) to the side of an anode A.sub.1.
As in FIG. 1, a variable resistor is connected to the side of anode A.sub.2. When a resistor which is connected between beam spot S and anode A.sub.1 has a resistance R.sub.1, and a resistor which is connected between the beam spot S and anode A.sub.2 has a resistance R.sub.2, and the above-mentioned variable resistor 2 has a resistance R.sub.3, the ratio I.sub.1 /I.sub.2 of the photocurrents I.sub.1, I.sub.2 which are output from anode A.sub.1 and anode A.sub.2 is given by EQU I.sub.1 /I.sub.2 =(R.sub.2 +R.sub.3)/R.sub.1 ( 1)
Therefore, as a beam spot S moves near an optical axis away from anode A.sub.1, the above-mentioned resistance R.sub.2 decreases, and resistance R.sub.1 increases. For the same reason, the ratio I.sub.1 /I.sub.2 decreases, and when an object is at infinite distant position on an optical axis, the beam spot becomes smallest.
By setting the above-mentioned resistance R.sub.3 of variable resistor 2 where the ratio I.sub.1 /I.sub.2 is 1, the position of the spot on the optical axis at that time can be deemed as the substantial electrical center of position sensitive detectors PSD 1. In other words, by the simple electrical operation of adjusting the resistance R.sub.3 of variable resistor 2 the electrical center of a PSD 1 can be shifted to the side of anode A.sub.2.
In the above-mentioned prior art apparatus, there has been an inconvenience in some cases wherein the electrical adjustment can not necessarily be made. For example, when the electrical center of PSD 1 is positioned at the longer distance side with respect to the optical axis of the light receiving optical system, the adjustment can not be made since the variable resistor is connected in the path wherein a signal of long distance side passes. That is, the adjustment can not be made when an electrical center C is shifted to the side opposite to the case shown in FIG. 1.
Furthermore, as disclosed in FIG. 1, publication, the variable resistor is connected in the path wherein the signal of long distance side passes. Therefore, an effective light receiving face changes equivalently, and makes the inconvenience that the gradation of output characteristic curve of PSD 1 is undesirably changes.
Namely, in the above-mentioned prior art apparatus needed, some means for adjustment for changing gradation of the characteristic.